Oxycodone (Oxycontin®) is a therapeutic agent believed to produce analgesia through interaction with centrally-located opiate receptors. As such, oxycodone belongs to the therapeutic class of such agents that includes hydrocodone (Vicodin®), naltrexone (Nalorex®), oxymorphone (Numorphan®), and the naturally occurring opium constituents, codeine and morphine. These agents are thought to promote analgesia through agonism of the opiate μ-, δ-, and κ-subtypes with varying selectivity. The μ-subtype agonists exert the greatest antinociceptive activity followed by the 6-subtype agonists. The κ-agonists exert antinociceptive activity but also produce dysphoria. Tissue distribution patterns for these subtypes are not uniform and so agents lacking subtype selectivity may exhibit superior or inferior pharmacology based on the specific drugs tissue distribution patterns. Certain unnatural enantiomers of naturally occurring opioids also possess biological activity. For example, Dextorphan (dextro-morphine) is the unnatural enantiomer of morphine (levo-morphine) and has been shown to induce antianalgesia against levo-morphine-produced antinociception. Dextorphan is also a N-methyl-D-aspartate (NMDA) receptor antagonist, and studies have linked the NMDA receptor to glaucoma. Osborne et al., Surv. Ophthalmol., 1999, 43(1), S102-128.
